Biotransformation of oleanolic and maslinic methyl esters by Rhizomucor miehei CECT 2749.

The pentacyclic triterpenoids methyl oleanolate, methyl maslinate, methyl 3ß-hydroxyolean-9(11),12-dien-28-oate, and methyl 2α,3ß-dihydroxy-12ß,13ß-epoxyolean-28-oate were biotransformed by Rhizomucor miehei CECT 2749. Microbial transformation of methyl oleanolate produced only a 7ß,30-dihydroxylated metabolite with a conjugated 9(11),12-diene system in the C ring. Biotransformation of the substrate with this 9(11),12-diene system gave the same 7ß,30-dihydroxylated compound together with a 7ß,15α,30-trihydroxyl derivative. The action of this fungus (R. miehei) on methyl maslinate was more varied, isolating metabolites with a 30-hydroxyl group, a 9(11),12-diene system, an 11-oxo group, or an 12-oxo group. Microbial transformation of the substrate with a 12ß,13ß-epoxy function resulted in the isolation of two metabolites with 12-oxo and 28,13ß-olide groups, hydroxylated or not at C-7ß, together with a 30-hydroxy-12-oxo derivative. The structures of these derivatives were deduced by extensive and rigorous spectroscopic studies.